1. Field of the Invention
This invention relates to a 2-cycle engine and a watercraft having the engine installed therein.
2. Related Art
A conventional 2-cycle engine is operated such that fresh air is sucked into the crank chamber formed by the crank case, and the fresh air is fed into the combustion chamber formed between the cylinder head and the piston through a scavenging passage.
A conventional air-fuel mixture scavenging type sucks only fresh air into the crank chamber. In the air scavenging type, fuel is supplied to the combustion chamber in addition to the fresh air.
Conventional watercraft utilize a jet pump propulsion means driven by a 2-cycle engine as described above. Since a small 2-cycle engine delivers a high output, the engine is particularly useful in a small-sized watercraft.
In the case of the 2-cycle engine, since the fresh air sucked into the crank chamber is fed into the combustion chamber, an increased temperature in the crank chamber (i.e. the crank case) causes the temperature of the fresh air to increase. As the temperature of the fresh air increases, the amount of oxygen per unit volume of the engine is reduced, resulting in reduced combustion efficiency. This reduces the engine output.
Accordingly, a watercraft utilizing a conventional 2-cycle engine does not realize the expected high output from the 2-cycle engine.
It is an object of the present invention to provide a 2-cycle engine and a watercraft having the 2-cycle engine realizing a high engine output.